This invention relates to electrostatographic copying machines and, more particularly, to an improved magnetic brush apparatus for use in electrostatographic copying machines.
In the practice of xerography as described in U.S. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material on a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic plate is electrostatically charged uniformly over its surface, and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern or latent electrostatic image in conformity with the configuration of the original pattern.
The latent electrostatic image is developed by contacting it with a finely divided electrostatically attractable material, such as a resinous powder. The powder is held in the image areas by the electrostatic fields on the layer. Where the field is greatest, the greatest amount of material is deposited, and where the field is least, little or no material is deposited. Thus, a powder image is produced in conformity with the image of the original being reproduced. The powder image is subsequently transferred to a sheet of paper or other transfer member, and suitably affixed thereto to form a permanent copy.
After the powder image is transferred, some residual toner usually remains on the imaging surface. The removal of all or substantially all of such residual toner is important to high copy quality since unremoved toner may appear as the background in the next copying cycle. The removal of the residual toner remaining on the imaging surface after the transfer operation is carried out in a cleaning operation.
In present day commercial automatic copying and duplicating machines, the electrostatographic imaging surface, which may be in the form of a drum or belt, moves at high rates in timed unison relative to a plurality of processing stations around the drum or belt. This rapid movement of the electrostatographic imaging surface has required vast amounts of toner to be used during development period. Thus, to produce high quality copies, a very efficient development apparatus and background removal apparatus or cleaning apparatus are necessary. Conventional cleaning devices have not been entirely satisfactory in this respect. Most of the known cleaning devices usually become less efficient as they become contaminated with toner, which cannot be removed, thus necessitating frequent replacement of the cleaning device. As a result, valuable time is lost during "down time" while a change is being made. Also, the cost of the cleaning device increases the per copy cost in such an apparatus. Other disadvantages with the conventional "web" type or the "brush" type cleaning apparatus are known to the art. Similarly, deficiencies of conventional development apparatus also are known. Thus, there is a need for improved development and/or cleaning apparatuses.